SYNTAX ZX80 Vo1. 1 No. 2

SYNTAX ZX80'

A PUBLICATION OF THE HARVARD GROUP

VOL. 1 NO. 2 REPRINT ISSN 0273-2696 1980

NEW NEW 8K ROM PLUS PRINTER

Last month we announced a new
8K ROM chip from Sinclair for
about the first of the year. Now
Sinclair is revamping that chip.
The new -chip will support the low
cost printer Sinclair plans to
introduce next year. Sinclair
expects to retain all previously
announced functions and price.
Redesigning will delay production
a few weeks .

AUTHORIZED SOFTWARE

Image Computer Products of
Northbrook, IL, is the authorized
ZX80 software producer. They are
a division of The Image Producers,
Inc. , an advertising and marketing
agency. Besides ZX80 software,
Image writes for Apple II, TRS-80,
Sorcerer and Atari microcomputers.

Dick Schultz, sales manager,
says Image offers primarily game
cassettes and some utility and
math tapes. A cassette contains 2
to 4 programs and comes with an
instruction manual containing
listings and flowcharts for $6.95.

In cooperation with Sinclair
Research, Image now offers a ZX80
Computer Learning Lab, a system of
self-paced computer programs and
workbook lessons, designed for an
interactive learning experience.
New computer owners can learn
problem-solving and programming in
a hands-on approach.

Both the Learning Lab and a
complete ZX80 are available from
Sinclair by mail for $249. Image
sells the Learning Lab alone for
$49.95 — see catalog for details.

SOFTWARE CATALOGS AVAILABLE

Software catalogs from Image
Computer Products are hot off the
presses and available to ZX80 and
MicroAce owners.

New ZX80 owners will find the
catalog packed with their machine.
Owners who bought their ZX80 ' s
before the catalog was printed
will receive them in the mail from
Sinclair Research. MicroAce
owners can get a copy by writing
to Image Computer Products, 615
Academy Dr., Northbrook, IL,

60062, or calling 312/564-5060.

SINCLAIR SHIPMENTS PICK UP

Sinclair caught up with their
ZX80 shipping schedule in November
because production rates are up to
meet the demand. What does this
mean to ZX80 owners? If you must
return your ZX80 for replacement
under warranty, expect to receive
your new machine much faster than
you old one. According to Nigel
Searle of Sinclair, shipments now
turn around on a one day schedule,
so your new ZX80 will go right out
the door.

8K ROM PROGRAMS HERE ! !

Next month we'll bring you
tested and debugged programs to
run with the new 8K ROM. Our
technical staff has the only
prototype 8K ROM in the U.S. and
we're wording on programs so you
will be able to use your new ROM
immediately. We're especially
impressed by the graphics
capability and the PLOT-DRAW-
PRINT sequence.

1

NEW MODEM

MicroPeripheral Corp. will
introduce a modem for ZX80 and
MicroAce machines by 1 January
1981, enabling you to connect to
other computers by telephone. The
computer turns its electrical
signals into tones which are
carried through the phone lines.

Unlike most modems, this one
will plug right into the telephone
jack, so it needs no acoustic
coupler. Direct connection gives
you clearer signal reception and
transmission.

Acoustic couplers attach to
the telephone handset and transmit
sound. Unfortunately, the modem
will transmit any sound it hears,
including background noise.

MicroPeripheral ' s modem
works at 300 baud (30 characters
per second) in both answer and
originate modes . An interface
decodes the bus on the chassis
rear, eliminating the need for an
RS232 adapter.

Perhaps the most exciting use
for this new accessory, according
to Don Stoner of MicroPeripheral,
is becoming part of the giant
nation-wide computer networks such
as The SOURCE or Micronet. You
can access government data bases
like the National Health Library
in Bethesda, or free public
bulletin boards. These systems
are compatible between several
kinds of computers , so you can
communicate with a vast number o f
people and machines. For a list
of regional systems, write to:

Donald Stoner

Customer Service

MicroPeripheral Corp.

Box 529

Mercer Island, WA 98040
(More information about The SOURCE
and Micronet in a later issue.)

At press time, Sinclair has
16K RAMs in production, available
in January after FCC approval.

EXTENDED ZX80 SERVICE CONTRACTS

Sinclair now offers extended
service contracts to ZX80 owners .
$25 per year will cover all parts
and labor and return shipment of
the unit. (You ship the machine
prepaid to Sinclair and they pay
the return postage.) For further
information, contact Sinclair
Research Ltd, 50 Staniford St. ,
Boston, MA, 02114.

OUR POLICY ON CONTRIBUTED MATERIAL

SNYTAX ZX80 invites you to express opinions
related to the ZX80 and the newsletter. We will print,
as space allows, letters discussing items of general
interest. Of course, we reserve the right to edit letters
to a suitable length and to refuse publication of any
material.

We welcome program listings for all levels of
expertise. Programs can be for any fun or useful
purpose. We will test run each one before publishing
it, but we will not debug programs; please send only
workable listings.

In return for your listing, we will pay you a token
fee of $2.00 per program we use. This payment gives
us the nonexclusive right to use that program in any
form, world-wide. This means you can still use it, sell
it, or give it away, and so can we.

We will consider submissions of news and
hardware or software reviews. Please keep articles
short (50-100 words). Again, we reserve the right to
edit accepted articles to a suitable length. We will pay
7 cents per 6 characters, including spaces and
punctuation, for accepted articles.

If you want us to return your original program
listing or article, please include a self-addressed,
stamped envelope. Otherwise, we cannot return
submitted material.

SYNTAX ZX80 is published monthly by

The Harvard Group, RD 2, Box 457, Bolton Road,
Harvard, MA 01451. Telephone 617 / 456-3661.
Subscription rates: 12 issues, $25.

Single issues, $4 each.

© The Harvard Group, 1980. All rights reserved.
Photocopying prohibited.

SYNTACTIC SUM™ is a trademark of
Syntax ZX80 , Inc. , and The Harvard
Group. All rights reserved.

2

MULTIPLICATION EXERCISE

This is a program I wrote to
help my daughter practice her
multiplication. It asks for the
multiplier (any number up to 3276)
and then presents 5 problems,
randomly choosing a number from 1
to 10. You get two tries to
answer correctly. After the
second try, the machine gives you
the right answer with the next
problem. At the end, it displays
the number correct and then you
can re-execute the program. This
program uses IK memory, so you can
add more descriptive information
as memory becomes available.

10 PRINT "HI. WHAT IS YOUR
NAME?"

20 INPUT A$

30 CLS

40 PRINT "OK, ";A$ ; " ENTER
MULTIPLIER. "

50 INPUT A
60 LET B=0
70 DIM X(5)

80 FOR J=1 TO 5
90 LET C=RND(100)

100 IF C>10 THEN LET C=C/10

110 LET X(J-1)=C

120 GO SUB 500

130 INPUT E

140 FOR L=1 TO 2

150 PRINT E

160 PRINT "THAT IS ";

170 IF NOT E=A*C THEN PRINT "IN

» l

i80 PRINT "CORRECT"

190 IF E=A*C THEN GO TO 250
200 IF L=2 THEN GO TO 260
210 PRINT "PLEASE TRY AGAIN."

220 INPUT E
230 GO SUB 500
240 NEXT L
250 LET B=B+1

260 PRINT "PRESS (NEWLINE) TO C
ONTINUE"

270 INPUT B$

280 NEXT J
285 LET J=J-1
290 GO SUB 500
300 P&INT A*X(4)

310 IF B >1 THEN GO TO 340
320 PRINT "BETTER TRY AGAIN,

330

340

350

360

370

380

390

*Tt I f

400

410

420

430

440

0

GO TO 380

IF B 5 THEN GO TO 370
PRINT "EXCELLENT, ";

GO TO 380

PRINT "NOT BAD, ";

PRINT A$

PRINT "YOU GOT ”;B;" CORREC

INPUT B$

CLS

PRINT "WANT TO TRY AGAIN?"
INPUT B$

IF CODE(B$)=62 THEN GO TO 3

450 CLS

460 PRINT "OK, ";A$;". THANKS
FOR"

470 PRINT "PLAYING WITH ME."

480 PRINT "SEE YOU NEXT TIME."
490 STOP
500 CLS

510 PRINT "MULTIPLY BY ";A
520 FOR K=1 to J
530 PRINT X(K-l);" X ";A;" = ";
540 IF NOT K=J THEN PRINT X(K-1
)*A

550 NEXT K
560 RETURN

SYNTACTIC SUM = -5144

Pete Cone, Davenport, IA

Image Computer Products wants
people to write ZX80 programs. For
author's guide, contact A1 Baker,
program director at Image.

MAKE -DO CONNECTORS

At SYNTAX we use a Radio Shack
connector. Their solderless edge-
card, 40-pin connector (#276-1558)
usually picks up all the contacts
we need. We also use 40- conductor ,
insulation displacement, ribbon
cable and mount the connector with
a metal- jawed vise. We open .the
connector ends with a small burr in
a hobby grinder. (Put a piece of
ciSPtuit board between the contacts
to prevent damage while cutting
end slots.) We terminate the

cable with an experimenter board
so we can simply plug into the
contact strips with wire jumpers
to the prototype board.

3

CASSETTE EAVESDROPPER

Use this simple circuit to
listen to your programs as they
save and load or to search for
programs on tape without pulling
the earphone cord and adjusting
the volume control each time.

The circuit consists of one
3.5 mm (0.125 inch) phone plug
wired to a 3.5 mm miniature phone
jack with another 3.5 mm phone
jack wired in parallel through a
1KX1 resistor . Build it into any
type of holder (a Radio Shack
project box is neat and
inexpensive) , although a metal
housing helps avoid TV
interference. Using a small
coaxial cable (rather than
separate conductors) for the wire
to the cassette plug further
avoids interference.

Once you build the device,
plug the phone plug into the
cassette earphone jack, an
earphone into the jack with the
resistor ^ and the ZX80 into the
other jack. Now you can listen to
your tapes through the earphone
with the volume set to maximum,
even if the ZX80 is listening too.

TIP

RING

lKOhm >
\ Watt >

To cassette
ear jack

O TIP

RING

TIP RING

Paul Holzchuher called to
tell a strange story. His ZX80
worked fine on the dining room
table, but on an aluminum table
it wouldn't load prerecorded or
newly recorded tapes. Raising it
off the table with books was no

help. A wooden table cured the
oroblem. When you have trouble
reloading programs , move your ZX80
to a non-conducting surface.

SEASON'S GREETINGS

Here is our personalized
holiday greeting to you, courtesy
of your.ZX80 or MicroAce. With a
little clever substitution in
lines 450- 640, you can adapt this
listing to produce your own video
Christmas card.

49 GO TO 100

50 FOR 1=1 to LM
60 PRINT "

70 NEXT I
80 RETURN
99 STOP

100 FOR N=2 TO 16
110 LET M=2* (N/2) - 1
120 LET LM=16-M
130 GO SUB 50

140 FOR J=16-M+l to 16+M-l
150 LET Y=51+RND(M)

160 IF Y=52 THEN LET X=Y
170 IF Y>52 THEN LET X=Y-51
180 IF Y>62 THEN LET X=222
190 PRINT CHR$ (X) ;

200 NEXT J
210 PRINT " "

220 NEXT N
400 LET LM=15
410 GO SUB 50
420 PRINT "U"

450 LET A$="Z"

465 LET D$="TAX"

480 LET K$="0"

485 LET N$=" "

500 LET LM=9
510 GO SUB 50

520 PRINT "HAPPY HOLIDAYS"

530 LET LM=12
540 GO SUB 50

560 PRINT "A";A$;N$;"K";K$;N$;"
E" ; K$

580 LET LM=13
590 GO SUB 50
600 PRINT "SYN";D$

620 LET LM=14
630 GO SUB 50
640 PRINT A$ ; "X" ; 5*4**2
SYNTACTIC SUM = -27631

4

COMPU- CALENDAR

This three-part program
returns correct day name, changes
Gregorian dates to corresponding
Julian day numbers , and computes
total days between any two dates
from Jan. 1 AD to Feb. 2300.

To use, type the month number
(NL) , day number (NL) , and four-
digit year (NL) . ZX80 returns the
correct day name, followed by a
prompt. Type J (NL) and it prints
the equivalent Julian day number.
(Julian days begin at GMT noon on
each day and count days from noon,
January 1, 4713 BC.)

You can also calculate the
number of days between two dates .
Enter the earlier one first, using
J (NL) to compute JD, then enter
the second date but just hit (NL)
instead of J (NL) to request total
days between the 2 dates.

Note that the ZX80 correctly
reads out JD numbers in millions ,
thousand and units, but blanks
leading zeros in each group. When
reporting total days , sometimes
the program displays thousands of
days as 1000 too high, followed by
negative hundreds; just add them.
For example: A read out of 2,-825
means total days = 1,175.

To exit the program, enter
numeral zero (NL) as the month.

Otis Imboden, Washington, D.C.

Note : This program takes leap

years into account, but as written
cannot display them. — AZ

10 PRINT "COMPU- CAL"

15 CLEAR

20 PRINT "ENTER MO /DY/ YEAR"

30 INPUT M
40 IF M=0 THEN STOP
50 INPUT D
55 INPUT Y
57 CLS

62 PRINT "YOUR DATE (" ; M; ; D;

' t / M . Y«. " ) .

68 IF Y<1900 OR (Y=1900 AND M<

3) THEN LET D=D+1

69 IF Y "1800 OR (Y=1800 and M<
3) THEN LET D=D+1

70 IF M>2 THEN GO TO 90
80 LET Y=Y- 1

85 LET M=M+13
87 GO TO 91

90 LET M=M+1

91 IF Y>2199 THEN LET D=D- 1
93 IF Y >2099 THEN LET D=D-1

100 LET A=Y*3+7200

110 LET B=(Y*6)+(M*3)+98

120 LET C=(Y*5)+((M*6)/10)

130 LET D=D+(Y/4)+C+2

135 LET L=l+A/ 10000

136 LET A=A- (10000* (A/ 10000) )
145 LET T=(A/10)+(B/100)+(D/100

0)

147 LET U=(100*(A-10*(A/10)))+(
10*(B-(100*(B/100)))+(D-1000*(D/
1000 )))

148 LET T=T+U/ 1000

149 LET U=U- (1000- (U/ 1000))

150 LET Z=2+L+(T*-1)+U
155 LET Z=Z-(7*(Z/7))

157 IF Z<0 THEN LET Z=Z+7

158 GO SUB (Z*2)+160

159 GO TO 179

160 PRINT "SATUR";

161 RETURN

162 PRINT "SUN";

163 RETURN

164 PRINT "MON";

165 RETURN

166 PRINT "TUES";

167 RETURN

168 PRINT "WEDNES";

169 RETURN

170 PRINT "THURS";

171 RETURN

172 PRINT "FRI";

173 RETURN

174 GO TO 160
179 PRINT "DAY"

181 INPUT J$

182 IF J$="J" THEN GO TO 195

186 IF T-S<1 THEN GO TO 188

187 PRINT T-S;",";

188 PRINT U-W;" TOTAL DAYS"

190 GO TO 15

195 LET S=T
197 LET W=U

199 PRINT " JD=" ; L ; " , " ; T ; " , " ; U
210 GO TO 20
SYNTACTIC SUM = 22279

5

COMPARISON BETWEEN THE SINCLAIR ZX30 AND THE TRS-80 COLOR COMPUTER

ITEM

SINCLAIR :

ZX80

TRS-80 COLOR

SINCLAIR W/8K ROM

Price

$200

$400

$240

Max size of array

255

mem- limit

mem- limit

Max # of dimensions

1

1

mem- limit

Digits of accuracy

5 integer

9 floating

9 . 5 floating

Range of numbers

+/- 32767

IE- 38 to IF, +38

9E-44 to 1. 1E+43

Max string length

mem- limit

255

mem- limit

Max size str array

no string

arrays

mem- limit

mem- limit

# of str dimensions

no string

arrays

1

mem- limit

# unique var names

mem- limit

936

mem- limit

# unique str names

26

936

26

Range of state #'s

1-9999

0-63999

1-9999

Comma spacing

8

16

16

# of comma fields

4

2

2

Str. data req "'s

no data stmnt

no

yes

Filenames (length)

no

8

mem- limit

Display size

25 x 32

16 x 32

22x32

Editor type

1 line scrn 6c list

none

1 line scrn 6c lis

Point of E switch

none

1 E-3 6c 1 E+9

1 E-6 6c 1 E+13

Use DEG/ RAD/ GRAD

none

RAD

RAD

Printer available?

no

yes

yes

Graphics resolution

none

64 x 32

64 x 44

Graphics origin

none

top left

bottom left

Colors available?

no

8

no

Joysticks avail?

no

yes

no

String concat

no

yes (+)

yes (+)

Cassette data I/O

no

yes

no

Mult stmnts/line

no

yes (:)

no

Uses ASCII

no

yes

no

Display w/o stop

no

yes

yes

Kbd readable

no

yes

yes

Protectable memory

no

yes

yes

Internal clock

p&p

no

P&P

ARE THE FOLLOWING FUNCTIONS INCLUDED?

** or uparrow

X

X

ABS & INT 6c SGN

ABS only

X

X

NOT & AND 6c OR

X

X

X

SIN 6c COS

SIN only

X

FRE/ FREE /MEM

X

X

VAL

X

X

LEN

X

X

SEG$/MID$ or equiv.

X

X

LEFT$ 6c RIGHT$

X

X

TAB

X

X

EOF

X

TAN 6c ATN

X

ASN 6c ACS

X

LOG/LN

LN

EXP 6c SQR/SQRT

X

PI

X

POINT

X

JOYSTK

X

6

ITEM

SINCLAIR ZX80

TRS-80 COLOR SINCLAIR W/8K ROM

ARE THE FOLLOWING STATEMENTS SUPPORTED?

RANDOMIZE X NOT NEEDED

FOR with STEP X

GET/INKEY$ X

PRINT AT X

READ & DATA X

RESTORE X

PLOT/ SET X

UNPLOT/ RESET X

INPUT# /PRINT# X

OPEN X

CLOSE X

AUDIO ON/OFF X

ON . . . GOSUB X

ON . . . GOTO X

IF. . .THEN. . .ELSE X

END X

SOUND (make noise) X

PRINT USING/TO
WAIT (time delay)
DRAW/ LINE
UNDRAW/ UNLINE
PAUSE
SCROLL

X

X

X

X

X

X

X

X

X

X

X

X

X

X

ARE THE FOLLOWING COMMANDS SUPPORTED?

LLIST X
SKIPF X
MOTOR ON /OFF X

ALL THREE MACHINES USE:

* String comparisons in an IF statement

* Immediate mode

* Dynamic DIM

* Double quotes (") for literal strings

* An output line width of 32 characters

* Operators + , *, and /

* LET , PRINT , INPUT , GOTO , IF . . . THEN , GOSUB , RETURN ,
FOR... NEXT, STOP, CLEAR/CLR, CLS , and REM statements

* PEEK, POKE, USR/EXEC , ASC/CODE, CHR$ , and STR$ function

* RUN, CONTINUE, LIST, NEW, SAVE, and LOAD commands

»

NONE OF THE MACHINES USE:

* MAT statements

* High speed cassette search

* Available floppy disks

NOTE: A / between choices
indicates either fulfills
category, while & requires both.

NOTE: P&P indicates tnat a simple
PEEK and POKE operation performs a
function not supported in system.

7

KEY TO COMPARISON CHARTS

• Range of numbers — greatest and
smallest no. system can express.

• Output line width — greatest
no. of characters on one output
display line.

• Comma spacing — width of comma
print fields .

• # of comma fields — no. of
comma print fields across one
display line.

• Str data req "'s — do strings

in data statements require quotes?

• Editor type — what kind of
editor does system use? (1 line
scrn means a single line screen
editor, list means listing is on
screen while editing. )

• Point of E switch — no. at
which system switches to display
in scientific notation.

• Use DEG/RAD/GRAD — how does
system measure angles?

• Graphics resolution — using
system plot commands (4K & program
can plot 64 x 48 from top left) .

• String concat — can system
append one string to another?

• Cassette data I/O — can system
store data (as opposed to
programs) on cassette tape?

• Uses ASCII — does system use
American Standard Code for
Information Interchange?

• Display w/o stop — can system
display something and continue
without any user interaction?

• Display size — height and width
of display in characters.

• Kbd readable — can system read
keyboard without stopping?

• Protectable memory — can a
section of memory be protected so
that machine language programs may
be stored there?

• USR/EXEC — equivalent
functions, transfer control to a
machine language program.

• POINT — returns whether or not

a certain graphics point is lit on
the screen.

• FRE/ FREE /MEM — return amount of
memory not used by program.

• RANDOMIZE — reseeds random
number generator.

• PRINT USING/TO— print no.
according to a specific format.

• FOR with STEP — extended form
of a FOR... NEXT statement to
specify an increment.

• END — signals end of program.

• BEEP — tells system to sound a
beeper to notify user.

• SOUND — tells the system to
make one of 255 sounds.

• GET/ INKEY$— read keyboard
without stopping.

• PRINT AT — prints information
at a certain screen position.

• WAIT — pause for a certain
programmable length of time.

• READ & DATA — reads nos . or
strings from list of information
after DATA statement and puts it
in variables.

• RESTORE — resets data list so
same data may be read in again.

• DRAW — draws a line on screen.

• PLOT/ SET — turns on screen
pixel .

• UNDRAW — opposite of DRAW.

• UNPLOT/RESET —opposite of PLOT.

• INPUT # — reloads all variables
in mempry from tape.

• PRINT # — stores all variables
in memory on tape.

• PAUSE — causes program to stop
for a moment and display output.

• SCROLL — causes all lines on
screen to move up one.

• SAVE/CSAVE — stores program on
cassette tape.

• LOAD/CLOAD — reloads program
from cassette tape.

• SKIPF — skips a file on tape.

%

• Dynamic DIM — array sizing
using a variable: DIM A(G) .

Syntactic Sums are an easy
way to check your program
typing for errors. Look
for our Syntactic Sum
program in SYNTAX, Feb. 81.

8

DEAR EDITOR:

The ZX80's black-on-white
video output is somewhat hard to
read. Most computers have a black
background with white letters.

There is a simple way to reverse
the ZX80 video output.

The video input to the RF
modulator comes from an exclusive
OR gate. One input to this gate
is the sync signal and the other
is the data. The data input comes

from pin 7 of_ IC9 , a 74LS165.

This is the Q output of the
parallel to serial converter. On
the bottom side of the PC board
near IC9 are 3 points marked A, B,
and C. A goes to the exclusive OR
gate, B to the Q output_(pin 9) of
IC9 , and C goes to the Q (inverted)

output (pin 7) . Presently
A is connected to C. To reverse
the output, break the connection
between A and C and make a new one
between A and B. Or you could
install a switch to switch between
the 2 different outputs.

Thanks for your magazine. It
should be a big help to all ZX80
owners in the future.

Brent Dix, Cedar City, UT

■ 4r ■ ■ . . . .

Here is a TAB subroutine
listing. It causes the display to
tab to any column, 1-32 left to
right. Just give COLTAB a value
corresponding to the desired
column number and insert a
subroutine call in your program.

900 GO TO 2000
999 REM TAB

1000 IF COLTAB >32 THEN RETURN
1005 LET ITAB=PEEK(16420) - (34-CO
LTAB)

1010 IF PEEK(16420) <2 THEN LET I
TAB=33- (34- COLTAB)

1015 IF ITAB < 1 THEN RETURN
1020 LET JTAB=1
1030 PRINT " " ;

1040 IF JTAB=ITAB THEN RETURN
1050 LET JTAB=JTAB+1
1055 GO TO 1030

1060 REM AS CONTINUING PART OF

1061 REM "PRINT ; " "GO SUB 1000"

1062 REM CAUSES TAB TO COLUMN

1063 REM IN "COLTAB" (1-32,

1064 REM LEFT TO RIGHT)

1065 REM "COLTAB NOT CLEARED.

1066 REM "COLTAB" MUST ALLOW

1067 REM SPACE FOR ALL

1068 REM INFORMATION PRINTED.

2000 STOP

(Listing appears exactly as on a
TV screen. In line 1005, COLTAB
is one word, as is ITAB in line
1010. --AZ)

To add another tab setting,
add a ; to the end of your first
print command, then assign another
value to COLTAB. Insert another
GO SUB and PRINT statement and the
display will print in two columns.

William Herron, San Diego, CA

- - - - I,----. - ■

I have an engineering
background but am a raw beginner
when it comes to computers. Could
you put me in touch with other
San Diego area ZX80 owners so that
I could contact them to exchange
ideas and questions?

H.S. Wake, San Diego, CA

714/455-1370

To respect your privacy, we will
not print subscriber names and
numbers, unless you request that
your name or number appear. --AZ)

Congratulations on the first
issue of SYNTAX ZX80. My ZX80
programs just fit in memory, but
there is not enough left to handle
variables or display. Machine
language programs run faster and
use less memory, but I don't grasp
the essentials of this method.

How about an article or series on
machine language? I look forward
to future issues of SYNTAX.

Mark Paulkus , New Britain, CT
Coming up.--AZ

9

HOW TO WIRE A BIG KEYBOARD

Although the ZX80 has many
fine features, some people
complain about the small pads of
the touch keyboard that comes with
it. But this is not a serious
problem. The ZX80 uses a matrixed
keyboard, so you can easily add a
bigger, parallel keyboard.

"Matrixed" means each key
connects two wires, one for the
key row, the other the key column.
Sinclair's matrix uses 8 rows and
5 columns which connect to 13
readily available points on the
circuit board. Two pins descend
from each key: When you depress
the key, the pins make electrical
contact, connecting an IC pin with
the anode of a diode. This tells
the computer which key you hit.

When you look for keyboards
at electronic surplus houses , try
to get these features :

• exchangeable key caps.

• molded block keyboards that
come off circuit boards easily.

• caps with changeable legends.

• a circuit board matrix nearly
matching the ZX80 matrix.

Unless you're sure you can
overcome the problems, avoid these
keyboards :

• mechanical types.

• ASCII encoded.

• separate switches on PC board.

• Hall effect keys.

• brushes wiping printed contacts.

• capacitive keyboards.

Just wire your big matrixed
keyboard in parallel with the
existing one. Use standard
single-pole, normally open
keyswitches. Wire duplicate keys,
such as "shift," in parallel so
both will function. If your big
keyboard has a numeric pad, wire
each switch in parallel with the
number keys above the letter keys.
Use a continuous length of

wire-wrap wire to daisy-chain one
contact of each switch in each
column. Do the same for the other
switch contact in each row. Just
push the insulation aside using
the stripper of a wire-wrap tool.

All components are clearly
labelled on the ZX80 board. You
must: wire both pins for each key.
On the following chart, D3--D10
represent the anodes of the diodes
on the front of the PC board. (Look
for the diode symbol under the
diodes. The anode is at the broad
end of the triangle.) Looking at
the top of IC10, the pin nearest
the IC10 label is pin 1. Pin 16
is directly across from pin 1.

Connect your keyswitches as
shown in the following diagram.

As shown for key "1", each key
connects to the line below it and
the line to its right. That is,
wire key 1 to diode 6 and to pin
10 of IC10.

1

1

2

3

i

4

8

9

1

1

4

5

6

7

0

1

1

U— T\ 7

DO

Q

r

W

E

R

T

Y

U

I

0

P

Du

A-

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S

D

F

G

H

J

K

L

NEW

Do

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SHF

tv n

z

X

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. 1

N

M

SPC

Dy

D3

TCI 0 PI

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1 L

J

4-

1

U

i

1

DID

IC10 PIN L
IC10 PIN U
IC10 PIN 1(
IC10 PIN (

1 . . .

)

)

3

For quick removal, use eight
spring-loaded test clips for diode
connections and parallel IC10 with
a 16-pin proto-clip. Ribbon cable
makes a good-looking interconnect.

ANSWER TO CRYPTOQUOTE PUZZLE

"Who chooses to cotnpete with
machines accepts the conditions of
s lavery"- -Norbert Weiner

lO

SUBROUTINES— SUPER STEP-SAVERS

Last month we talked about
FOR-NEXT loops as a way to repeat
steps. This time we'll look at
subroutines, which tell the
computer to repeat a series of
steps each time you call them.

Subroutines are mini-
programs; they execute a series of
steps apart from the main program.
In essence, you tell the computer,
"Go do those steps and then come
back here and proceed with the
main program." The ZX80 remembers
where it was and returns to the
following line after executing the
subroutine. You can call the
subroutine many times from your
main program, but you need type it
only once.

Suppose you want to use the
TAB subroutine listing on page 17.
The subroutine is lines 999-1055,
but you need a whole program to
fit around it. Say you want to
print a list of dollar figures as
part of an accounting program you
are writing. TAB only helps
instruct the computer to display
your data in tabular columns. You
must still tell what to do with
the data you enter. So when you
get to line 140, where you want to
display results in columns, call
up TAB us ing GO SUB :

140 GO SUB 999

•

The computer jumps to 999 and then
executes steps until it hits the
RETURN command, then hops back to
the line after the GO SUB from
which it left the main program.
When you again want TAB, say at
line 290, write:

290 GO SUB 999

Again, it executes steps 999 to
1055 but this time it returns to
the line following 290. TAB uses
IF. . .THEN RETURN statements to
jump back. Insert a RETURN at
every endpoint of the subroutine.

One more point : As the
computer goes through the program
steps, it eventually comes to line
999 and tries to carry out the
subroutine again. Trouble starts
when it prints data you didn't
want and then it hits RETURN and
has no where to go. The ZX80
gives you an error code 7 , meaning
it Jiit a RETURN with no
corresponding GO SUB. To avoid
this, insert a jump (GO TO) step:

900 GO TO 2000

999 REM TAB

1055 GO TO 1030
2000 STOP

Now the machine never runs into
the subroutine unless directed
there by a GO SUB because the GO
TO in 900 causes it to jump over
the subroutine to the STOP step.

You can GO SUB backwards and
forwards — the ZX80 can jump to a
subroutine with a larger or
smaller line number, so you can
insert your subroutine anywhere in
your program. Wherever you put
it, remember the GO SUB, RETURN
and GO TO steps.

Use subroutines whenever you:

• repeat 3 or more program lines.

• reuse a complex line you might
mistype ..

• want 2 processing steps to
always be identical.

NEW MAGAZINE

SYNC, published by Creative
Computing , is due to hit the
stands in January. Devoted to the
Sinclair and MicroAce machines ,
SYNC will concentrate on software
and applications, according to
publisher Dave Ahl. Subscriptions
are $10 for 6 issues, $15 Canadian
and foreign surface. SYNC, 39 E.
Hanover Ave., Morris Plains, NJ ,
07950 (800) 631-8112.

To SAVE (and therefore LOAD) your
programs faster, type CLEAR (NL)
before saving. This tells the
ZX80 not to save any variables.

1 1

BIG CHARACTER PROGRAM

Make your video characters 8
times bigger using ROM character
images and substituting graphic
symbols for screen dots. Change
lines 140 & 160 for other symbols.

5

DIM C(4)

7

LET K=0

10

INPUT A$

11

PRINT

15

LET K=K+1

17

IF K< 3 THEN GO

TU

20

18

CLS

19

LET K=1

20

FOR X=1 to 4

30

LET C (X) =C0DE (A$)

40

LET A$=TL$(A$)

50

NEXT X

60

FOR L=1 TO 8

70

FOR D=1 TO 4

80

LET Q=PEEK(C (D)

*8+358 3+L)

100

LET B=8

110

LET B=B- 1

115

IF B<0 THEN GO

TO

200

120

IF Q<2**B THEN

GO

TO 160

130

LET Q=Q-2**B

140

PRINT CHR$ (128)

%

3

150

GO _ 110

160

PRINT ' " ;

170

GO TO 110

200

NEXT D

210

NEXT L

220

GO TO 10

SYNTACTIC SUM = 25918

Operation: RUN (NL) . Respond

to Drompt with 4 characters & (NL)
for 1st line. Next 4 letters go
on 2nd line. Next 4 clear screen
before printing on first line. To
exit, hit (NL) break.

ZX80 AND MICROACE BUS PINOUT

PIN

BOTTOM

TOP

23

NC

NOT

REFSH

22

A4

NOT

Ml

21

A5

NOT

RESET

20

A6

NOT

BUSRQ

19

A7

NOT

WAIT

18

A8

NOT

BUSAK

17

A9

NOT

WR

16

A10

NOT

RD

15

All

NOT

IORQ

14

A12

NOT

MREQ

13

A13

NOT

HALT

12

A14

NOT

NMI

11

A15

NOT

INT

10

A3

D4 '

9

A2

D3 '

8

A1

D5 '

7

A0

D6 '

6

NOT CLOCK

D2 '

5

0 VOLT

Dl'

4

0 VOLT

DO'

3

SLOT

SLOT

2

9 VOLT

RAM

CS 1

1

5 VOLT

D7 '

Top is component side; bottom,
solder side. This is a Z-80 bus.

Tl-E

H\RV\RD

GROLP

Bolton Road, Harvard, Mass. 01451

CD